This was the last flight of my S500. It took me some time to figure out what exactly went wrong. It turned out to be the battery. The Hudson X4Pro 7000mHa Lipo. It seems this battery is set up with a surge protection circuit that has a habit of kicking in for no reason. This is what happened here. Just before LOS, I had turned the aircraft 180deg causing a loss of the video feed. When this happened I tripped the Failsafe Return to Home RTH function. This is when the battery failed. The sound you hear when the S500 is falling is the sound of the props "Wind Milling". There was NO power to the UAV.
